Sodium cobalt oxide hydrate

Abstract

Disclosed is a hydrated sodium-cobalt oxide exhibiting superconductivity at low temperatures. The hydrated sodium-cobalt oxide comprises a plurality of CoO 2 layers each having edge-sharing CoO 6 octahedra, and a combination of two water molecule layers and a single sodium ion layer, interposed between the adjacent CoO 2 layers, wherein the distance between the adjacent CoO 2 layers is in the range of 9.5 to 10.5 Å. The present invention provides the first cobalt oxide exhibiting superconductivity. The hydrated sodium-cobalt oxide has an extremely large distance between cobalt layers, and includes highly diffusible sodium ions and water molecules between the layers. Thus, based on high ability of ion-exchanging with various ion species and molecules, the hydrated sodium-cobalt oxide can be effectively used as a precursor for synthesizing materials through ion exchanging.

1 . A hydrated sodium-cobalt oxide comprising a plurality of CoO 2  layers each having edge-sharing CoO 6  octahedra, and a combination of two water molecule layers and a single sodium ion layer, which is interposed between the adjacent CoO 2  layers.  
     
     
         2 . The hydrated sodium-cobalt oxide as defined in  claim 1 , wherein the distance between the adjacent CoO 2  layers is in the range of 9.5 to 10.5 Å.  
     
     
         3 . A hydrated sodium-cobalt oxide, which is represented by the following general formula:  
         Na x CoO 2 ·yH 2 O, wherein 0<x≦0.4, and 1.0≦y≦2.0.  
     
     
         4 . The hydrated sodium-cobalt oxide as defined in either one of  claims 1  to  3 , which exhibits superconductivity at a temperature of 5 K or less.  
     
     
         5 . A method of producing a hydrated sodium-cobalt oxide, comprising; 
 synthesizing, from a sodium compound and a cobalt compound, Na x CoO 2  (0.5≦x≦1.0) which comprises a plurality of CoO 2  layers each having edge-sharing CoO 6  octahedra, and a single sodium ion layer interposed between the adjacent CoO 2  layers;    deintercalating a part of the sodium ions from said Na x CoO 2 , and    then intercalating a water molecule between the adjacent CoO 2  layers.